With reference to FIG. 1, a cable television (CATV) network 1 in accordance with the present invention includes a head end 2, which transmits RF cable television and other data and information signals downstream over cables 3 via hubs 4 and nodes 6 to customer receiving equipment 7 in customer buildings 5. Amplifiers 8 are positioned throughout the network 1 to amplify the downstream signals to ensure the transmitted signals reach the customer receiving equipment 7 with a desired quality of service (QoS). Each of the amplifiers 8 has a built in automatic gain control (AGC) circuit 11 to adjust the level of their gain (up or down).
Initially, each amplifier 8 is set with a nominal setting that is appropriate for the respective amplifier 8 in the network 1. Normally, a field technician would go to each amplifier 8 during the first installation and balance out the amplifiers 8 so the signal levels leaving each amplifier 8 are correct. If the AGC circuit 11 in an amplifier 8 is faulty, that amplifier 8 will cause level fluctuation on all the channels coming out thereof. Moreover, if a modulator in the headend 2 has a problem with its output level, that particular channel produced by the modulator will have level fluctuation. That level fluctuation will cause the receiving equipment 7, which receives the digital channel, to exercise their own AGC algorithms to hold the power level of the digital channel signal constant for demodulation. Some receiver equipment 7 is better able to hold the power level of the digital channel signals steady, thereby compensating for power fluctuations in the digital channel signals and making any problems with the digital channel signal difficult to detect. However, customer receiver equipment 7 tends to be on the inexpensive side, and thus often fails or has much worse bit errors than test equipment, whereby the test equipment would fail to detect problems the customer receiver equipment is experiencing.
An object of the present invention is to overcome the shortcomings of the prior art by providing a method and test equipment for informing a technician how “hard” the AGC loop in the test equipment 21 is working, e.g. required gain fluctuations, to hold the power level of the incoming signal steady for demodulation, thereby indicating that the level of the digital channel carrier is not stable. A hard working AGC loop indicates that either an amplifier 8 in the CATV network 1 has a faulty AGC circuit 11 or a modulator in the headend 2 is malfunctioning. A technician can use the test equipment 21, in accordance with the present invention, to check the AGC stress at the proper points in the network 1 to determine whether the problem is related to a faulty AGC circuit 11 or a malfunctioning modulator in the headend 2.